a. Field of the Invention
The instant invention relates generally to localization systems for determining position utilizing localization fields and more particularly to a localization system having dynamic adaptive respiration compensation with automatic gain control.
b. Background Art
Numerous technologies have been developed to permit the determination of the location of a catheter inside of a beating heart. U.S. Pat. No. 5,697,377 to Wittkampf discloses a system that uses orthogonal currents (i.e., along three axes—X, Y and Z) injected into the body using body surface electrodes (patches) to localize the catheter. In Wittkampf's system, an electrode located on the catheter measures voltages arising from the three injected currents, which are then processed to resolve the X, Y and Z axis coordinates defining the position of the electrode and hence also the position of the catheter tip.
An improved localization system may be seen by reference to U.S. Pat. No. 7,263,397 issued to Hauck et al. (hereinafter “Hauck”) entitled METHOD AND APPARATUS FOR CATHETER NAVIGATION AND LOCATION AND MAPPING IN THE HEART, assigned to the common assignee of the present invention, and hereby incorporated by reference in its entirety. Hauck discloses a medical system for determining the location of electrodes within the body utilizing localization fields. Like the system of Wittkampf, the system of Hauck injects currents into the body using surface “patch” electrodes. However, Hauck discloses a variation that involves injecting currents using non-orthogonal pairs of patch electrodes (i.e., defining dipoles) wherein drive axes are synthesized from the resulting measurements and from which the electrode positions are ultimately determined.
A common use of the catheter position is for displaying a representation of the catheter with respect to cardiac geometries or other imaging of a region of interest in which the catheter is located. However, patient respiration and cardiac activity can make the displayed catheter appear to “move” with respect to the acquired cardiac geometries (or imaging), which are static. In order to reduce the apparent motion of the catheter with respect to these static geometries (or imaging) and provide a clinician with a more stable view, it is known to use motion compensation to correct for the effects introduced by patient respiration and cardiac activity.
In this regard, Hauck discloses a respiration compensation approach that involves determining a respiration motion artifact, which in turn is then subtracted from the calculated (uncompensated) electrode position. The respiration compensation method improves accuracy. Hauck further discloses determining the respiration compensation artifact upon a user direction during an electrophysiological (EP) study. In a commercial embodiment, the respiration compensation may be determined at any time but this can be done only at the user's explicit direction. However, during the course of an EP study or medical procedure, a patient's respiration pattern may change or the position of the catheter within the heart may change, such that the previously-determined (static) compensation may no longer provide the initial high level of accuracy. Additionally, during the course of an EP study or medical procedure, there may occur sudden changes in a so-called patch impedance measurement (i.e., a measured parameter underlying the localization and compensation approaches disclosed in Hauck). For example, a clinician may temporarily place his or her hand on a body surface electrode (patch), which temporarily alters the measured patch impedance, thereby affecting the localization/compensation calculations.
There is therefore a need for a system and method for motion compensation (e.g., respiration, cardiac) that minimizes and/or eliminates one or more of the above problems.